Oxytocin

Gene switches make prairie voles fall in love Epigenetic changes affect neurotransmitters that lead to pair-bond formation. Zoe Cormier 02 June 2013 Adv Exp Med Biol. 1998;449:215-24. Oxytocin, vasopressin, and the neuroendocrine basis of pair bond formation. Insel TR1, Winslow JT, Wang Z, Young LJ. Author information Abstract Several lines of evidence support a role […]

Gene switches make prairie voles fall in love

Epigenetic changes affect neurotransmitters that lead to pair-bond formation.

02 June 2013


Adv Exp Med Biol. 1998;449:215-24.

Oxytocin, vasopressin, and the neuroendocrine basis of pair bond formation.

Abstract

Several lines of evidence support a role for oxytocin and vasopressin in complex social behaviors, including parental care, sex behavior, and aggression. Recent studies in a monogamous mammal, the prairie vole, suggest an additional role for both peptides in the formation of pair bonds. Central administration of oxytocin facilitates and administration of an oxytocin antagonist inhibits partner preference formation in female prairie voles. Conversely, vasopressin facilitates and a V1a receptor antagonist inhibits pair bonding in males. A potential cellular basis for these effects is the species-specific pattern of expression of oxytocin and V1a receptor in reward pathways of the prairie vole brain. At a molecular level, comparative sequencing of the oxytocin and V1a receptors reveals species differences in the promoter sequences that may guide regional expression in the brain. Transgenic mice created with the 5′ flanking region of the prairie vole oxytocin receptor gene demonstrate that sequencing in this region influence the pattern of expression within the brain. The unique promoter sequences of the prairie vole OTR and V1a receptor genes and the resulting species-specific pattern of regional expression provide a potential molecular mechanism for the evolution of pair bonding behaviors and a cellular basis for monogamy.


Oxytocin (Oxt) is a hormone, neuropeptide, and medication.[3][4] As a medication, it is used to cause contraction of the uterus in order to start labor or increase the speed of labor, and to stop bleeding following delivery.[3] For this purpose, it is given either byinjection into a muscle or into a vein.[3]

The use of oxytocin as a medication can result in excessive contraction of the uterus that can cause distress in an unborn baby. Common side effects in the mother include nausea and a slow heart rate. Serious side effects include water intoxication with an excessive dose and uterus rupture. Allergic reactions may also occur.[3]

Oxytocin is normally produced in the hypothalamus.[5][6] It plays a role in social bonding, sexual reproduction in both sexes, and during and after childbirth.[7] Oxytocin is released into the bloodstream as a hormone in response to stretching of the cervix anduterus during labor and with stimulation of the nipples from breastfeeding.[6] This helps with birth, bonding with the baby, and milk production.[6][8]

Oxytocin was discovered in 1952.[9] It is on the World Health Organization’s List of Essential Medicines, the most important medications needed in a basic health system.[10] As of 2014, the wholesale cost of the medication is US$0.1–0.56 per dose.[11]

Oxytocin has peripheral (hormonal) actions, and also has actions in the brain. Its actions are mediated by specific, oxytocin receptors. The oxytocin receptor is a G-protein-coupled receptor that requires magnesium and cholesterol. It belongs to therhodopsin-type (class I) group of G-protein-coupled receptors.

Studies have looked at oxytocin’s role in various behaviors, including orgasm, social recognition, pair bonding, anxiety, and maternal behaviors.[12]

The peripheral actions of oxytocin mainly reflect secretion from the pituitary gland. The behavioral effects of oxytocin are thought to reflect release from centrally projecting oxytocin neurons, different from those that project to the pituitary gland, or that are collaterals from them.[13] Oxytocin receptors are expressed by neurons in many parts of the brain and spinal cord, including the amygdala,ventromedial hypothalamus, septum, nucleus accumbens, and brainstem.

  • Letdown reflex: In lactating (breastfeeding) mothers, oxytocin acts at the mammary glands, causing milk to be ‘let down’ intosubareolar sinuses, from where it can be excreted via the nipple.[14] Suckling by the infant at the nipple is relayed by spinal nerves to the hypothalamus. The stimulation causes neurons that make oxytocin to fire action potentials in intermittent bursts; these bursts result in the secretion of pulses of oxytocin from the neurosecretory nerve terminals of the pituitary gland.
  • Uterine contraction: Important for cervical dilation before birth, oxytocin causes contractions during the second and third stages oflabor. Oxytocin release during breastfeeding causes mild but often painful contractions during the first few weeks of lactation. This also serves to assist the uterus in clotting the placental attachment point postpartum. However, in knockout mice lacking the oxytocin receptor, reproductive behavior and parturition are normal.[15]
  • Social behavior[16][17] and wound healing: Oxytocin is also thought to modulate inflammation by decreasing certain cytokines. Thus, the increased release in oxytocin following positive social interactions has the potential to improve wound healing. A study by Marazziti and colleagues used heterosexual couples to investigate this possibility. They found increases in plasma oxytocin following a social interaction were correlated with faster wound healing. They hypothesized this was due to oxytocin reducing inflammation, thus allowing the wound to heal more quickly. This study provides preliminary evidence that positive social interactions may directly influence aspects of health.[18] According to a study published in 2014, silencing of oxytocin receptor interneurons in the medial prefrontal cortex (mPFC) of female mice resulted in loss of social interest in male mice during the sexually receptive phase of the estrous cycle.[19]
Oxytocin evokes feelings of contentment, reductions in anxiety, and feelings of calmness and security when in the company of the mate.[20] This suggests oxytocin may be important for the inhibition of the brain regions associated with behavioral control, fear, and anxiety, thus allowing orgasm to occur. Research has also demonstrated that oxytocin can decrease anxiety and protect against stress, particularly in combination with social support.[21]
  • Due to its similarity to vasopressin, it can reduce the excretion of urine slightly. In several species, oxytocin can stimulate sodium excretion from the kidneys (natriuresis), and, in humans, high doses can result in hyponatremia.
  • Oxytocin and oxytocin receptors are also found in the heart in some rodents, and the hormone may play a role in the embryonal development of the heart by promotingcardiomyocyte differentiation.[22][23] However, the absence of either oxytocin or its receptor in knockout mice has not been reported to produce cardiac insufficiencies.[15]
  • Modulation of hypothalamic-pituitary-adrenal axis activity: Oxytocin, under certain circumstances, indirectly inhibits release of adrenocorticotropic hormone and cortisol and, in those situations, may be considered an antagonist of vasopressin.[24]
  • Autism: Oxytocin may play a role in autism and may be an effective treatment for autism‘s repetitive and affiliative behaviors.[25] Oxytocin treatments also resulted in an increased retention of affective speech in adults with autism.[26] Two related studies in adults, in 2003 and 2007, found oxytocin decreased repetitive behaviors and improved interpretation of emotions. More recently, intranasal administration of oxytocin was found to increase emotion recognition in children as young as 12 who are diagnosed with autism spectrum disorders.[27] Oxytocin has also been implicated in the etiology of autism, with one report suggesting autism is correlated with genomic deletion of the gene containing the oxytocin receptor gene (OXTR). Studies involving Caucasian and Finnish samples and Chinese Han families provide support for the relationship of OXTR with autism.[26][28] Autism may also be associated with an aberrant methylation of OXTR.[26] After treatment with inhaled oxytocin, autistic patients exhibit more appropriate social behavior.[29] While this research suggests some promise, further clinical trials of oxytocin are required to demonstrate potential benefit and side effects in the treatment of autism. As such, researchers do not recommend use of oxytocin as a treatment for autism outside of clinical trials.[30]
  • Nasally administered oxytocin has also been reported to reduce fear, possibly by inhibiting the amygdala (which is thought to be responsible for fear responses).[31] Indeed, studies in rodents have shown oxytocin can efficiently inhibit fear responses by activating an inhibitory circuit within the amygdala.[32][33] Some researchers have argued oxytocin has a general enhancing effect on all social emotions, since intranasal administration of oxytocin also increases envy and Schadenfreude.[34]
  • Trust is increased by oxytocin.[35][36][37] Disclosure of emotional events is a sign of trust in humans. When recounting a negative event, humans who receive intranasaloxytocin share more emotional details and stories with more emotional significance.[36] Humans also find faces more trustworthy after receiving intranasal oxytocin. In a study, participants who received intranasal oxytocin viewed photographs of human faces with neutral expressions and found them to be more trustworthy than those who did not receive oxytocin.[35] This may be because oxytocin reduces the fear of social betrayal in humans.[38] Even after experiencing social alienation by being excluded from a conversation, humans who received oxytocin scored higher in trust on the Revised NEO Personality Inventory.[37] Moreover, in a risky investment game, experimental subjects given nasally administered oxytocin displayed “the highest level of trust” twice as often as the control group. Subjects who were told they were interacting with a computer showed no such reaction, leading to the conclusion that oxytocin was not merely affecting risk aversion.[39] When there is a reason to be distrustful, such as experiencing betrayal, differing reactions are associated with oxytocin receptor gene (OXTR) differences. Those with the CT haplotype experience a stronger reaction, in the form of anger, to betrayal.[40]
  • Oxytocin affects social distance between adult males and females, and may be responsible at least in part for romantic attraction and subsequent monogamous pair bonding. An oxytocin nasal spray caused men in a monogamous relationship, but not single men, to increase the distance between themselves and an attractive woman during a first encounter by 10 to 15 centimeters. The researchers suggested that oxytocin may help promote fidelity within monogamous relationships.[41] For this reason, it is sometimes referred to as the “bonding hormone”. There is some evidence that oxytocin promotes ethnocentric behavior, incorporating the trust and empathy of in-groups with their suspicion and rejection of outsiders.[16] Furthermore, genetic differences in the oxytocin receptor gene (OXTR) have been associated with maladaptive social traits such as aggressive behaviour.[42]
  • Affecting generosity by increasing empathy during perspective taking: In a neuroeconomics experiment, intranasal oxytocin increased generosity in the Ultimatum Game by 80%, but had no effect in the Dictator Game that measures altruism. Perspective-taking is not required in the Dictator Game, but the researchers in this experiment explicitly induced perspective-taking in the Ultimatum Game by not identifying to participants into which role they would be placed.[43] Serious methodological questions have arisen, however, with regard to the role of oxytocin in trust and generosity.[44]
Empathy in healthy males has been shown to be increased after intranasal oxytocin[45][46] This is most likely due to the effect of oxytocin in enhancing eye gaze.[47] There is some discussion about which aspect of empathy oxytocin might alter – for example, cognitive vs. emotional empathy.[48]
  • Certain learning and memory functions are impaired by centrally administered oxytocin.[49] Also, systemic oxytocin administration can impair memory retrieval in certain aversive memory tasks.[50] Interestingly, oxytocin does seem to facilitate learning and memory specifically for social information. Healthy males administered intranasal oxytocin show improved memory for human faces, in particular happy faces.[51][52] They also show improved recognition for positive social cues over threatening social cues[53][54] and improved recognition of fear.[55]
  • Sexual activity: The relationship between oxytocin and human sexual response is unclear. At least two uncontrolled studies have found increases in plasma oxytocin at orgasm – in both men and women.[56][57] Plasma oxytocin levels are notably increased around the time of self-stimulated orgasm and are still higher than baseline when measured five minutes after self arousal.[56] The authors of one of these studies speculated that oxytocin’s effects on muscle contractibility may facilitate sperm and egg transport.[56]
In a study measuring oxytocin serum levels in women before and after sexual stimulation, the author suggests it serves an important role in sexual arousal. This study found genital tract stimulation resulted in increased oxytocin immediately after orgasm.[58] Another study reported increases of oxytocin during sexual arousal could be in response to nipple/areola, genital, and/or genital tract stimulation as confirmed in other mammals.[59] Murphy et al. (1987), studying men, found oxytocin levels were raised throughout sexual arousal with no acute increase at orgasm.[60] A more recent study of men found an increase in plasma oxytocin immediately after orgasm, but only in a portion of their sample that did not reach statistical significance. The authors noted these changes “may simply reflect contractile properties on reproductive tissue”.[61]
  • Bonding: In the prairie vole, oxytocin released into the brain of the female during sexual activity is important for forming a monogamous pair bond with her sexual partner. Vasopressin appears to have a similar effect in males.[62] Oxytocin has a role in social behaviors in many species, so it likely also does in humans. In a 2003 study, both humans and dog oxytocin levels in the blood rose after five to 24 minutes of a petting session. This possibly plays a role in the emotional bonding between humans and dogs.[63]
  • Maternal behavior: Female rats given oxytocin antagonists after giving birth do not exhibit typical maternal behavior.[64] By contrast, virgin female sheep show maternal behavior toward foreign lambs upon cerebrospinal fluid infusion of oxytocin, which they would not do otherwise.[65] Oxytocin is involved in the initiation of maternal behavior, not its maintenance; for example, it is higher in mothers after they interact with unfamiliar children rather than their own.[66]
  • Drug interactions: According to some studies in animals, oxytocin inhibits the development of tolerance to various addictive drugs (opiates, cocaine, alcohol), and reduceswithdrawal symptoms.[67] MDMA (ecstasy) may increase feelings of love, empathy, and connection to others by stimulating oxytocin activity primarily via activation of serotonin5-HT1A receptors, if initial studies in animals apply to humans.[68] The anxiolytic Buspar (buspirone) may produce some of its effects via 5-HT1A receptor-induced oxytocin stimulation as well.[69][70]
  • Preparing fetal neurons for delivery: Crossing the placenta, maternal oxytocin reaches the fetal brain and induces a switch in the action of neurotransmitter GABA from excitatory to inhibitory on fetal cortical neurons. This silences the fetal brain for the period of delivery and reduces its vulnerability to hypoxic damage.[71]
  • Romantic attachment: In some studies, high levels of plasma oxytocin have been correlated with romantic attachment. For example, if a couple is separated for a long period of time, anxiety can increase due to the lack of physical affection. Oxytocin may aid romantically attached couples by decreasing their feelings of anxiety when they are separated.[20]
  • Feeding: Recent evidence has suggested that oxytocin neurons in the para-ventricular hypothalamus in the brain may play a key role in suppressing appetite under normal conditions and that other hypothalamic neurons may trigger eating via inhibition of these oxytocin neurons. This population of oxytocin neurons are absent in Prader-Willi syndrome, a genetic disorder that leads to uncontrollable feeding and obesity, and may play a key role in its pathophysiology.[72]
  • Group-serving dishonesty/deception: In a carefully controlled study exploring the biological roots of immoral behavior, oxytocin was shown to promote dishonesty when the outcome favored the group to which an individual belonged instead of just the individual.[73]
  • Intergroup bonding: Oxytocin can increase positive attitudes, such as bonding, toward individuals with similar characteristics, who then become classified as “in-group” members, whereas individuals who are dissimilar become classified as “out-group” members. Race can be used as an example of in-group and out-group tendencies because society often categorizes individuals into groups based on race (Caucasian, African American, Latino, etc.). One study that examined race and empathy found that participants receiving nasally administered oxytocin had stronger reactions to pictures of in-group members making pained faces than to pictures of out-group members with the same expression.[74] This shows that oxytocin may be implicated in our ability to empathize with individuals of different races and could potentially translate into willingness to help individuals in pain or stressful situations. Moreover, individuals of one race may be more inclined to help individuals of the same race than individuals of another race when they are experiencing pain. Oxytocin has also been implicated in lying when lying would prove beneficial to other in-group members. In a study where such a relationship was examined, it was found that when individuals were administered oxytocin, rates of dishonesty in the participants’ responses increased for their in-group members when a beneficial outcome for their group was expected.[75] Both of these examples show the tendency to act in ways that benefit people with which one feels is part of their social group, or in-group. Oxytocin is not only correlated with the preferences of individuals to associate with members of their own group, but it is also evident during conflicts between members of different groups. During conflict, individuals receiving nasally administered oxytocin demonstrate more frequent defense-motivated responses toward in-group members than out-group members. Further, oxytocin was correlated with participant desire to protect vulnerable in-group members, despite that individual’s attachment to the conflict.[76] Similarly, it has been demonstrated that when oxytocin is administered, individuals alter their subjective preferences in order to align with in-group ideals over out-group ideals.[77] These studies demonstrate that oxytocin is associated with intergroup dynamics. Further, oxytocin influences the responses of individuals in a particular group to those of another group. The in-group bias is evident in smaller groups; however, it can also be extended to groups as large as one’s entire country leading toward a tendency of strong national zeal. A study done in the Netherlands showed that oxytocin increased the in-group favoritism of their nation while decreasing acceptance of members of other ethnicities and foreigners.[16] People also show more affection for their country’s flag while remaining indifferent to other cultural objects when exposed to oxytocin.[78] It has thus been hypothesized that this hormone may be a factor in xenophobic tendencies secondary to this effect. Thus, oxytocin appears to affect individuals at an international level where the in-group becomes a specific “home” country and the out-group grows to include all other countries.

The amygdalae

The amygdalae (singular: amygdala; /əˈmɪɡdələ/; also corpus amygdaloideum; Latin, from Greek ἀμυγδαλή, amygdalē, ‘almond’, ‘tonsil’[1]) are two almond-shaped groups of nuclei located deep and medially within the temporal lobes of the brain in complex vertebrates, including humans.[2] Shown in research to perform a primary role in the processing of memory, decision-making, andemotional reactions, the amygdalae […]

The amygdalae (singular: amygdala; /??m??d?l?/; also corpus amygdaloideum; Latin, from Greek ????????, amygdal?, ‘almond’, ‘tonsil’[1]) are two almond-shaped groups of nuclei located deep and medially within the temporal lobes of the brain in complex vertebrates, including humans.[2] Shown in research to perform a primary role in the processing of memory, decision-making, andemotional reactions, the amygdalae are considered part of the limbic system.[3]

Amygdalar development

There is considerable growth within the first few years of structural development in both male and female amygdalae. Within this early period, female limbic structures grow at a more rapid pace than do males. Amongst female subjects, the amygdala reaches its full growth potential approximately 1.5 years before the peak of male development. The structural development of the male amygdala occurs over a longer period than in women. Despite the early development of female amygdalae, they reach their growth potential sooner than males, whose amygdalae continue to develop. The larger relative size of the male amygdala may be attributed to this extended developmental period.

In addition to longer periods of development, other neurological and hormonal factors may contribute to sex-specific developmental differences. The amygdala is rich in androgen receptors – nuclear receptors that bind to testosterone. Androgen receptors play a role in the DNA binding that regulates gene expression. Though testosterone is present within the female hormonal systems, women have lower levels of testosterone than men. The abundance of testosterone in the male hormonal system may contribute to development. In addition, the grey matter volume on the amygdala is predicted by testosterone levels, which may also contribute to the increased mass of the male amygdala.

In addition to sex differences, there are observable developmental differences between the right and left amygdala in both males and females. The left amygdala reaches its developmental peak approximately 1.5–2 years prior to the right amygdala. Despite the early growth of the left amygdala, the right increases in volume for a longer period of time. The right amygdala is associated with response to fearful stimuli as well as face recognition. It is inferred that the early development of the left amygdala functions to provide infants the ability to detect danger.[12]

In childhood, the amygdala is found to react differently to same-sex versus opposite-sex individuals. This reactivity decreases until a person enters adolescence, where it increases dramatically at puberty.[13]

Gender distinction

The amygdala is one of the best-understood brain regions with regard to differences between the sexes. Larger male than female amygdalae have been demonstrated in children ages 7–11,[14] in adult humans,[15] and in adult rats.[16]

In addition to size, other differences between men and women exist with regards to the amygdala. Subjects’ amygdala activation was observed when watching a horror film andsubliminal stimuli. The results of the study showed a different lateralization of the amygdala in men and women. Enhanced memory for the film was related to enhanced activity of the left, but not the right, amygdala in women, whereas it was related to enhanced activity of the right, but not the left, amygdala in men.[17] One study found evidence that on average, women tend to retain stronger memories for emotional events than men.[18]

The right amygdala is also linked with taking action as well as being linked to negative emotions,[19] which may help explain why males tend to respond to emotionally stressful stimuli physically. The left amygdala allows for the recall of details, but it also results in more thought rather than action in response to emotionally stressful stimuli, which may explain the absence of physical response in women.

Emotional learning

In complex vertebrates, including humans, the amygdalae perform primary roles in the formation and storage of memories associated with emotional events. Research indicates that, during fear conditioning, sensory stimuli reach the basolateral complexes of the amygdalae, particularly the lateral nuclei, where they form associations with memories of the stimuli. The association between stimuli and the aversive events they predict may be mediated by long-term potentiation,[22][23] a sustained enhancement of signaling between affected neurons.[24] There have been studies that show that damage to the amygdala can interfere with memory that is strengthened by emotion. One study examined a patient with bilateral degeneration of the amygdala. He was told a violent story accompanied by matching pictures and was observed based on how much he could recall from the story. The patient had less recollection of the story than patients with functional amygdala, showing that the amygdala has a strong connection with emotional learning.[25]

Memories of emotional experiences imprinted in reactions of synapses in the lateral nuclei elicit fear behavior through neuronal connections with the central nucleus of the amygdalae and the bed nuclei of the stria terminalis (BNST). The axon terminals from sensory neurons form synapses with dendritic spines on neurons from the central nucleus.[26] The central nuclei are involved in the genesis of many fear responses such as defensive behavior (freezing or escape responses), autonomic nervous system responses (changes in blood pressure and heart rate/tachycardia), neuroendocrine responses (stress-hormone release), etc. Damage to the amygdalae impairs both the acquisition and expression of Pavlovian fear conditioning, a form of classical conditioning of emotional responses.[24]

The amygdalae are also involved in appetitive (positive) conditioning. It seems that distinct neurons respond to positive and negative stimuli, but there is no clustering of these distinct neurons into clear anatomical nuclei.[27][28] However, lesions of the central nucleus in the amygdala have been shown to reduce appetitive learning in rats. Lesions of the basolateral regions do not exhibit the same effect.[29] Research like this indicates that different nuclei within the amygdala have different functions in appetitive conditioning.[30][31]

Memory modulation

The amygdala is also involved in the modulation of memory consolidation. Following any learning event, the long-term memory for the event is not formed instantaneously. Rather, information regarding the event is slowly assimilated into long-term (potentially lifelong) storage over time, possibly via long-term potentiation. Recent studies suggest that the amygdala regulates memory consolidation in other brain regions. Also, fear conditioning, a type of memory that is impaired following amygdala damage, is mediated in part by long-term potentiation.[22][23]

During the consolidation period, the memory can be modulated. In particular, it appears that emotional arousal following the learning event influences the strength of the subsequent memory for that event. Greater emotional arousal following a learning event enhances a person’s retention of that event. Experiments have shown that administration of stress hormones to mice immediately after they learn something enhances their retention when they are tested two days later.[32]

The amygdala, especially the basolateral nuclei, are involved in mediating the effects of emotional arousal on the strength of the memory for the event, as shown by many laboratories including that of James McGaugh. These laboratories have trained animals on a variety of learning tasks and found that drugs injected into the amygdala after training affect the animals’ subsequent retention of the task. These tasks include basic classical conditioning tasks such as inhibitory avoidance, where a rat learns to associate a mild footshock with a particular compartment of an apparatus, and more complex tasks such as spatial or cued water maze, where a rat learns to swim to a platform to escape the water. If a drug that activates the amygdalae is injected into the amygdalae, the animals had better memory for the training in the task.[33] If a drug that inactivates the amygdalae is injected, the animals had impaired memory for the task.

Buddhist monks who do compassion meditation have been shown to modulate their amygdala, along with their temporoparietal junction and insula, during their practice.[34] In anfMRI study, more intensive insula activity was found in expert meditators than in novices.[35] Increased activity in the amygdala following compassion-oriented meditation may contribute to social connectedness.[36]

Amygdala activity at the time of encoding information correlates with retention for that information. However, this correlation depends on the relative “emotionalness” of the information. More emotionally arousing information increases amygdalar activity, and that activity correlates with retention. Amygdala neurons show various types of oscillationduring emotional arousal, such as theta activity. These synchronized neuronal events could promote synaptic plasticity (which is involved in memory retention) by increasing interactions between neocortical storage sites and temporal lobe structures involved in declarative memory.[37]

Research using Rorschach test blot 03 finds that the number of unique responses to this random figure links to larger sized amygdalae. The researchers note, “Since previous reports have indicated that unique responses were observed at higher frequency in the artistic population than in the nonartistic normal population, this positive correlation suggests that amygdalar enlargement in the normal population might be related to creative mental activity.”[38]

Neuropsychological correlates of amygdala activity

Early research on primates provided explanations as to the functions of the amygdala, as well as a basis for further research. As early as 1888, rhesus monkeys with a lesioned temporal cortex (including the amygdala) were observed to have significant social and emotional deficits.[39] Heinrich Klüver and Paul Bucy later expanded upon this same observation by showing that large lesions to the anterior temporal lobe produced noticeable changes, including overreaction to all objects, hypoemotionality, loss of fear, hypersexuality, and hyperorality, a condition in which inappropriate objects are placed in the mouth. Some monkeys also displayed an inability to recognize familiar objects and would approach animate and inanimate objects indiscriminately, exhibiting a loss of fear towards the experimenters. This behavioral disorder was later named Klüver-Bucy syndrome accordingly,[40] and later research proved it was specifically due to amygdala lesions. Monkey mothers who had amygdala damage showed a reduction in maternal behaviors towards their infants, often physically abusing or neglecting them.[41] In 1981, researchers found that selective radio frequency lesions of the whole amygdala caused Klüver-Bucy syndrome.[42]

With advances in neuroimaging technology such as MRI, neuroscientists have made significant findings concerning the amygdala in the human brain. A variety of data shows the amygdala has a substantial role in mental states, and is related to many psychological disorders. Some studies have shown children with anxiety disorders tend to have a smaller left amygdala. In the majority of the cases, there was an association between an increase in the size of the left amygdala with the use of SSRIs (antidepressant medication) or psychotherapy. The left amygdala has been linked to social anxiety, obsessive and compulsive disorders, and post traumatic stress, as well as more broadly to separation and general anxiety.[43] In a 2003 study, subjects with borderline personality disorder showed significantly greater left amygdala activity than normal control subjects. Some borderline patients even had difficulties classifying neutral faces or saw them as threatening.[44] Individuals with psychopathy show reduced autonomic responses, relative to comparison individuals, to instructed fear cues.[45] In 2006, researchers observed hyperactivity in the amygdala when patients were shown threatening faces or confronted with frightening situations. Patients with more severe social phobia showed a correlation with increased response in the amygdala.[46] Similarly, depressed patients showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces. Interestingly, this hyperactivity was normalized when patients were administered antidepressant medication.[47] By contrast, the amygdala has been observed to respond differently in people with bipolar disorder. A 2003 study found that adult and adolescent bipolar patients tended to have considerably smaller amygdala volumes and somewhat smaller hippocampal volumes.[48] Many studies have focused on the connections between the amygdala and autism.[49]

Studies in 2004 and 2006 showed that normal subjects exposed to images of frightened faces or faces of people from another race will show increased activity of the amygdala, even if that exposure is subliminal.[50][51] However, the amygdala is not necessary for the processing of fear-related stimuli, since persons in whom it is bilaterally damaged show rapid reactions to fearful faces, even in the absence of a functional amygdala.[52]

Recent research suggests that parasites, in particular toxoplasma, form cysts in the brain of rats, often taking up residence in the amygdala. This may provide clues as to how specific parasites may contribute to the development of disorders, including paranoia.[53]

Future studies have been proposed to address the role of the amygdala in positive emotions, and the ways in which the amygdala networks with other brain regions.[54]

Sexual orientation

Recent studies have suggested possible correlations between brain structure, including differences in hemispheric ratios and connection patterns in the amygdala, and sexual orientation. Homosexual men tend to exhibit more female-like patterns in the amygdala than heterosexual males do, just as homosexual females tend to show more male-like patterns in the amygdala than heterosexual women do. It was observed that amygdala connections were more widespread from the left amygdala in homosexual males, as is also found in heterosexual females. Amygdala connections were more widespread from the right amygdala in homosexual females, as in heterosexual males.[55][55][56]

Social interaction

Amygdala volume correlates positively with both the size (the number of contacts a person has) and the complexity (the number of different groups to which a person belongs) of social networks.[57][58] Individuals with larger amygdalae had larger and more complex social networks. They were also better able to make accurate social judgments about other persons’ faces.[59] The amygdala’s role in the analysis of social situations stems specifically from its ability to identify and process changes in facial features. It does not, however, process the direction of the gaze of the person being perceived.[60][61]

The amygdala is also thought to be a determinant of the level of a person’s emotional intelligence. It is particularly hypothesized that larger amygdalae allow for greater emotional intelligence, enabling greater societal integration and cooperation with others.[62]

The amygdala processes reactions to violations concerning personal space. These reactions are absent in persons in whom the amygdala is damaged bilaterally.[63]Furthermore, the amygdala is found to be activated in fMRI when people observe that others are physically close to them, such as when a person being scanned knows that an experimenter is standing immediately next to the scanner, versus standing at a distance.[63]

Aggression

Animal studies have shown that stimulating the amygdala appears to increase both sexual and aggressive behavior. Likewise, studies using brain lesions have shown that harm to the amygdala may produce the opposite effect. Thus, it appears that this part of the brain may play a role in the display and modulation of aggression.[64]

Fear

There are cases of human patients with focal bilateral amygdala lesions, due to the rare genetic condition Urbach-Wiethe disease.[65][66] Such patients fail to exhibit fear-related behaviors, leading one, Patient S.M., to be dubbed the “woman with no fear”. This finding reinforces the conclusion that the amygdala “plays a pivotal role in triggering a state of fear”.[67]

Alcoholism and binge drinking

The amygdala appears to play a role in binge drinking, being damaged by repeated episodes of intoxication and withdrawal.[68] Alcoholism is associated with dampened activation in brain networks responsible for emotional processing[clarification needed], including the amygdala.[69] Protein kinase C-epsilon in the amygdala is important for regulating behavioral responses to morphine, ethanol, and controlling anxiety-like behavior. The protein is involved in controlling the function of other proteins and plays a role in development of the ability to consume a large amount of ethanol.[70][71]

Anxiety

There may also be a link between the amygdala and anxiety.[72] In particular, there is a higher prevalence of females that are affected by anxiety disorders. In an experiment,degu pups were removed from their mother but allowed to hear her call. In response, the males produced increased serotonin receptors in the amygdala but females lost them. This led to the males being less affected by the stressful situation.

The clusters of the amygdala are activated when an individual expresses feelings of fear or aggression. This occurs because the amygdala is the primary structure of the brain responsible for flight or fight response. Anxiety and panic attacks can occur when the amygdala senses environmental stressors that stimulate fight or flight response.

The amygdala is directly associated with conditioned fear. Conditioned fear is the framework used to explain the behavior produced when an originally neutral stimulus is consistently paired with a stimulus that evokes fear. The amygdala represents a core fear system in the human body, which is involved in the expression of conditioned fear. Fear is measured by changes in autonomic activity including increased heart rate, increased blood pressure, as well as in simple reflexes such as flinching or blinking.

The central nucleus of the amygdala has direct correlations to the hypothalamus and brainstem – areas directly related to fear and anxiety. This connection is evident from studies of animals that have undergone amygdalae removal. Such studies suggest that animals lacking an amygdala have less fear expression and indulge in non-species-like behavior. Many projection areas of the amygdala are critically involved in specific signs that are used to measure fear and anxiety.

Mammals have very similar ways of processing and responding to danger. Scientists have observed similar areas in the brain – specifically in the amygdala – lighting up or becoming more active when a mammal is threatened or beginning to experience anxiety. Similar parts of the brain are activated when rodents and when humans observe a dangerous situation, the amygdala playing a crucial role in this assessment. By observing the amygdala’s functions, people can determine why one rodent may be much more anxious than another. There is a direct relationship between the activation of the amygdala and the level of anxiety the subject feels.

Feelings of anxiety start with a catalyst – an environmental stimulus that provokes stress. This can include various smells, sights, and internal feelings that result in anxiety. The amygdala reacts to this stimuli by preparing to either stand and fight or to turn and run. This response is triggered by the release of adrenaline into the bloodstream. Consequently, blood sugar rises, becoming immediately available to the muscles for quick energy. Shaking may occur in an attempt to return blood to the rest of the body. A better understanding of the amygdala and its various functions may lead to a new way of treating clinical anxiety.[73]

Posttraumatic stress disorder

There seems to be a connection with the amygdalae and how the brain processes posttraumatic stress disorder. Multiple studies have found that the amygdalae may be responsible for the emotional reactions of PTSD patients. One study in particular found that when PTSD patients are shown pictures of faces with fearful expressions, their amygdalae tended to have a higher activation than someone without PTSD.[74]

Political orientation

Amygdala size has been correlated with cognitive styles with regard to political thinking. A study found that “greater liberalism was associated with increased gray matter volume in the anterior cingulate cortex, whereas greater conservatism was associated with increased volume of the right amygdala.”[75]

Westermarck effect

The Westermarck effect, or reverse sexual imprinting, is a hypothetical psychological effect through which people who live in close domestic proximity during the first few years of their lives become desensitized to sexual attraction. This phenomenon was first hypothesized by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891) as one […]

The Westermarck effect, or reverse sexual imprinting, is a hypothetical psychological effect through which people who live in close domestic proximity during the first few years of their lives become desensitized to sexual attraction. This phenomenon was first hypothesized by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891) as one explanation for the incest taboo. Observations interpreted as evidence for the Westermarck effect have since been made in many places and cultures, including in the Israeli kibbutz system, and the Chinese Shim-pua marriage customs, as well as in biological-related families.

In the case of the Israeli kibbutzim (collective farms), children were reared somewhat communally in peer groups, based on age, not biological relation. A study of the marriage patterns of these children later in life revealed that out of the nearly 3,000 marriages that occurred across the kibbutz system, only fourteen were between children from the same peer group. Of those fourteen, none had been reared together during the first six years of life. This result suggests that the Westermarck effect operates during the period from birth to the age of six.[1]

When proximity during this critical period does not occur—for example, where a brother and sister are brought up separately, never meeting one another—they may find one another highly sexually attractive when they meet as adults or adolescents, according to the hypothesis of genetic sexual attraction. This supports the theory that the populations exhibiting the Westermarck effect became predominant because of the deleterious effects of inbreeding on those that didn’t.

Westermarck effect

The Westermarck effect, or reverse sexual imprinting, is a hypothetical psychological effect through which people who live in close domestic proximity during the first few years of their lives become desensitized to sexual attraction. This phenomenon was first hypothesized by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891) as one […]

The Westermarck effect, or reverse sexual imprinting, is a hypothetical psychological effect through which people who live in close domestic proximity during the first few years of their lives become desensitized to sexual attraction. This phenomenon was first hypothesized by Finnish anthropologist Edvard Westermarck in his book The History of Human Marriage (1891) as one explanation for the incest taboo. Observations interpreted as evidence for the Westermarck effect have since been made in many places and cultures, including in the Israeli kibbutz system, and the Chinese Shim-pua marriage customs, as well as in biological-related families.

In the case of the Israeli kibbutzim (collective farms), children were reared somewhat communally in peer groups, based on age, not biological relation. A study of the marriage patterns of these children later in life revealed that out of the nearly 3,000 marriages that occurred across the kibbutz system, only fourteen were between children from the same peer group. Of those fourteen, none had been reared together during the first six years of life. This result suggests that the Westermarck effect operates during the period from birth to the age of six.[1]

When proximity during this critical period does not occur—for example, where a brother and sister are brought up separately, never meeting one another—they may find one another highly sexually attractive when they meet as adults or adolescents, according to the hypothesis of genetic sexual attraction. This supports the theory that the populations exhibiting the Westermarck effect became predominant because of the deleterious effects of inbreeding on those that didn’t.

Doing Homework

In their article ‘“It’s Like Doing Homework” Academic Achievement Discourse in Adolescent Girls’ Fellatio Narratives’, April Burns, Valerie Futch and Deborah Tolman describe how young girls use norms surrounding academic achievement when making sense of their sexual behavior. It seems … Continue reading

In their article ‘“It’s Like Doing Homework” Academic Achievement Discourse in Adolescent Girls’ Fellatio Narratives’, April Burns, Valerie Futch and Deborah Tolman describe how young girls use norms surrounding academic achievement when making sense of their sexual behavior.

It seems that in cultures that have a dominant discourse of academic achievement, which “… frames the primary purpose of education in terms of the achievement of high grades and standardized test scores, rather than preparation for college, employment or civic participation”, girls can incorporate such values in other aspects of their lives as well, including their sexual behavior.

The authors found that girls tend to talk about engaging in sexual behavior such as oral sex, in a manner that resembles how they talk about doing homework and test-taking at school: it’s a job that needs to get done, that they need to practice to become good at, and that they expect to be evaluated for. Performance anxieties that girls may have about taking tests at school, including fears of failing and the need to perform (as) well (as others), may have entered girls’ sexual lives.

Girls’ narratives of their own sexual pleasure, a “positive” discourse of sexuality in relationship, or consequences of sexual behavior such as STIs, pregnancy or rape, were rare. Whereas the physical sexual satisfaction seemed to be of boys alone, girls’ satisfaction was the pleasure in a job done well, and correctly.

Burns, A., & Futch, V.A., & Tolman, D.L. (2011). “It’s Like Doing Homework” Academic Achievement Discourse in Adolescent Girls’ Fellatio Narratives Sexuality Research and Social Policy

sex, dinosaurs, and placoderms

A review of John A. Long’s “The Dawn of the Deed: The Prehistoric Origins of Sex,” a book that cleverly combines accounts of the paleontological discoveries of the first sexual organs and vertebrate embryos with a salacious description of the wild sexual practices throughout the animal world.

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A review of The Dawn of the Deed: The Prehistoric Origins of Sex, by John A. Long (University of Chicago Press, Chicago, 2012).

As I mentioned in last week’s post, we all know that subjects like sex and dinosaurs are guaranteed to get the public’s attention and interest, no matter what story you want to promote. Paleontologist and author Dr. John A. Long (formerly the Vice-President of Research and Collections at the Natural History Museum of Los Angeles County, but now back home in Australia as the Strategic Professor in Palaeontology at Flinders University in Adelaide) has cleverly woven a story about the wild sex lives of the animals kingdom as a hook to talk about his own research into the fossil fish (especially an extinct group called placoderms), which show the first evidence of internal fertilization, the oldest known vertebrate embryos, and the first copulatory structures.

One would think that a story about small extinct placoderms in nodules from the deserts of Western Australia would be a hard sell for a popular book, but Long pulls off the feat with aplomb. The heart of the book is filled with Long’s excitement about this research as he finds and uncovers these amazingly 3D fish fossils from the nodules of the Gogo beds, then compares them with fossils described from collections elsewhere in the world. He soon discovers that mysterious structures that were misidentified or ignored by previous fish paleontologists are actually pelvic claspers (long rodlike structures also found in the pelvic fins of modern sharks to aid them in copulation with females). Then he and his colleagues discover traces of tiny bones inside an adult placoderm that were misidentified as their last meal, but turn out to be embryos. We follow Long’s story as he works on this research until is it is accepted to be published in top journals like Nature. The discovery gets global coverage, and Long even takes part in big media events with a live uplink between the announcement in Australia and Queen Elizabeth of England (in a chapter called “Announcing Fossil Sex to the Queen”).

Surrounding this story of Long’s research into the earliest fish sex are chapters that review some of the wild and bizarre sexual practices among living animals. We find out all about how erotic asphyxiation works (first discovered in hanging victims that orgasmed  and ejaculated as they died), the prevalence of homosexual behavior in many groups of animals, and why certain ducks have the longest penises among any groups of vertebrates (longer than their entire body). In the final few chapters, Long reviews the evidence for the evolution of sex from the first sexually-reproducing organisms, to the incredible sexual feats of the arthropods. These include male barnacles, which have a penis eight times longer than their bodies, to the story of how the male bedbug stabs the body cavity of the female with his knife-like penis, and leaves the sperm packet inside her body, to the familiar accounts of how female praying mantises eat the male as he is copulating with her, and he keeps at it and does even better at copulation even though his head is gone. Long describes some of the bizarre sexual behavior of fishes, from the grunion running on the beach, to the deep-sea fish where the males attach to females and then degenerate into sperm organs and nothing more.There is a vivid account of sexual behavior in mammals, from the rough sex practiced by dolphin and orcas (the males will use their long penises in surprising ways), to the various types of sperm competition where one male secretes a plug in the female after copulation, but other males have penises which can remove the plug and replace the competitor’s sperm.

And of course, the million-dollar question: how did dinosaurs do it? Long begins with the story about how the first dinosaur leg bone fossil ever discovered was described as “Scrotum humanum” by Richard Brookes in 1763. He describes the legendary accounts of how eccentric British paleontologist Beverly Halstead demonstrated dinosaur mating behavior on the stage during a professional talk (something I heard about when I was a graduate student), showed slides of himself in the full Monty to demonstrate the proportions of the human penis, and had illustrations showing copulating dinosaurs in children’s books. Long discusses the practices of male lizards and snakes which have hemipenes (a penis forked into two branches, which pop out of their cloaca when inflated like a rubber glove turning inside out). Based on the types of sexual dimorphism seen in dinosaurs and the behaviors of their closest relatives, the birds and crocodiles, Long concludes that dinosaur males must have had a single penis (not hemipenes, or cloacal kissing), and probably copulated with males mounted behind (as do turtles and crocodilians). But as several other authors have also shown, this poses a problem for large sauropods, who would be putting their enormous weight largely on their two hind legs and whose heads must have stayed down during copulation or else they would have passed out from the difficulty of getting the blood all the way up to their brains if they raised their necks!

In short, Long’s book is a lively and uninhibited account of sexual behavior throughout the animal kingdom, and how we can learn about past sexual behavior from the fossil record. Unless you are prudish and can’t stand reading such material, the entire book is a short fun read that will keep your interest from beginning to end. As Jared Diamond wrote in his review of the book, “You are now holding a compromise between a book that you should carry hidden inside an opaque bag, and a sober, respectable scientific treatise. It’s a deliciously written account of the evolution of sex, in all its bizarre manifestations. Read, blush, and enjoy!”